R-F antenna apparatus for generating conical scan pattern

ABSTRACT

A four quadrant antenna is connected to r-f receiving and/or transmitting means by an arrangement including five 180* hybrid couplers (magic tee waveguides), a 90* hybrid coupler and a single 360* phase shifter. The branching arms of two of the 180* couplers are respectively connected to the four antenna quadrant elements while a third 180* coupler has its branching arms connected to the E-plane arms of the first mentioned couplers. The H-plane arms of the latter are connected to the branching arms of a fourth 180* coupler. Input/output to the circuit is coupled through a fifth 180* hybrid coupler which in turn is connected via its branching arms to the fourth 180* coupler and a 360* phase shifter. The latter is connected to the H-plane arm of the third 180* coupler through a 90* hybrid coupler, the latter also being connected to the E-plane arm of the fourth 180* coupler. Rotation of the phase shifter causes the axis of the antenna beam pattern to follow a path describing a cone. Modified arrangements include a duplexer connected to the fifth 180* hybrid coupler such that an r-f transmitter feeding the duplexer with signal pulses causes the antenna to broadcast corresponding pulses in either a scanned or a fixed beam pattern. A receiver also connected to the fifth 180* coupler operates during the intervals between transmission pulses to detect radiation received by the antenna from a conically scanned field.

United States Patent n 1 Barker l R-F ANTENNA APPARATUS FOR GENERATINGCONICAL SCAN PATTERN Jabus Barker, Utica, NY.

[73] Assignee: General Electric Company, Utica.

[22] Filed: Apr. 26, 1974 [21] Appl. No.: 464,430

[75} Inventor:

Primary ExaminerEli Lieberman [57] ABSTRACT A four quadrant antenna isconnected to r-f receiving and/or transmitting means by an arrangementincluding five 180 hybrid couplers (magic tee waveguides) a 90 hybridcoupler and a single 360 phase shifter l l July 1, 1975 The branchingarms of two of the I80 couplers are respectively connected to the fourantenna quadrant elements while a third 180 coupler has its branchingarms connected to the E-plane arms of the first mentioned couplers. TheH-plane arms of the latter are connected to the branching arms of afourth [80 coupler. Input/output to the circuit is coupled through afifth 180 hybrid coupler which in turn is connected via its branchingarms to the fourth I80" coupler and a 360 phase shifter. The latter isconnected to the H- plane arm of the third [80 coupler through a 90hybrid coupler. the latter also being connected to the E- plane arm ofthe fourth 180 coupler. Rotation of the phase shifter causes the axis ofthe antenna beam pattern to follow a path describing a cone. Modifiedarrangements include a duplexer connected to the fifth 180 hybridcoupler such that an r-f transmitter feeding the duplexer with signalpulses causes the antenna to broadcast corresponding pulses in either ascanned or a fixed beam pattern. A receiver also connected to the fifth180 coupler operates during the intervals between transmission pulses todetect radiation received by the antenna from a conically scanned field.

8 Claims, ll Drawing Figures R-F ANTENNA APPARATUS FOR GENERATINGCONICAL SCAN PATTERN BACKGROUND OF THE INVENTION The invention relatesto r-f antenna arrangements and, more particularly, to a phase-scannedantenna arrangement for scanning a beam through a conical scan pattern.The invention herein described was made in the course of or under acontract or subcontract thereunder, with the Department of Defense.

In the past, generation of conical patterns through the use ofstationary, phase-scanned multiple antenna arrangements has required theuse of multiple phase shifting or attenuation elements. One sucharrangement, for example, employs a four quadrant flat plate arrayantenna wherein each of the antenna quadrants is coupled to a single I/Odevice through a series of 180 hybrid couplers. A phase shifter isincluded in each portion of the circuit which connects to one of theantenna elements. The phase shifters are operated at a common frequencyby individual actuation inputs which are progressively offset by aquarter wavelength. The result is conical scanning of the antenna beampattern at a scan frequency equal to the common actuating frequency.

The requirement for four separate phase shifters makes such anarrangement complicated and expensive to manufacture due to thecomplexities of the phase shifters themselves and unless the shiftersare closely matched in operating characteristics a high degree of scanaccuracy is difficult to obtain.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of thepresent invention to provide an improved r-f antenna arrangement forproducing a phase-scanned conical beam pattern through use of relativelysimple and inexpensive circuit elements.

It is a further object to provide an improved r-f antenna arrangement ofthe type described which employs but a single phase shifting element.

Still a further object is to provide an improved r-f antenna arrangementof the type described which is capable of intermittent transmit andreceive operations wherein both such operations may utilize scanning orwherein only one of such operations undergoes scanning while the otherdoes not.

In accordance with the first aspect of the invention a four elementantenna is connected to an 180 hybrid coupler (magic tee) by a series ofcircuit elements including four additional 180 hybrid couplers, one 90hybrid coupler and a single 360 phase shifter. The four antenna elementsare respectively connected to the branching arms of two of theadditional 180 couplers. The latter have their E-plane arms connected tothe branching arms of another of the additional couplers and have theirH-plane arms connected to the branching arms of the fourth additional180 coupler. The U0 coupler has its branching arms connectedrespectively to the H-plane arms of the aforementioned third and fourth[80 couplers and to the phase shifter, the connection going to the thirdcoupler including the 360 phase shifter and the 90 hybrid coupler. Asecond port of the 90 coupler is connected to the E-plane arm of theaforementioned fourth additional [80 coupler. Rotation of the phaseshifter through 360 degrees scans the antenna beam pattern through aconical path.

In accordance with a second aspect of the invention the H-plane arm ofthe I/O coupler is connected to a receiver while a duplexer is insertedbetween the fourth additional 180 coupler and the associated branchingarm of the I/O coupler. A transmitter is connected to feed intermittentpulses to the antenna through the duplexer. The result is the emissionfrom the antenna of a fixed beam during the transmission cycles while inthe intervals between transmission pulses the receiver is fed energyfrom the antenna under the influence of the rotating phase shifter withthe result that the system is conically scanned in the receive mode butnot in the transmit mode. In a variation of this aspect of the invention the dupIexer/transmitter is inserted at the input to thereceiver resultng in the scanning of both transmit and receiver beampatterns.

These and other objects, features and advantages will be made apparentby the following description of preferred embodiments of the invention,the description being supplemented by drawings as follows:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective,semi-schematic view. par tially exploded, of an r-f antenna arrangementconstructed in accordance with the principles ofthe invention. Dashedlines are employed to represent conventional waveguide elements whichhave been omitted for purposes of simplifying the drawing.

FIG. 2 is a front elevation sectional view of the antenna taken alongline 22 of FIG. I.

FIG. 3 is a full front elevation view of the antenna.

FIG. 4 is a schematic circuit diagram of the antenna arrangement of FIG.I.

FIG. 5 is a schematic circuit diagram depicting one form of prior artantenna arrangement.

FIG. 6 is a perspective view of a portion of the antenna arrangement ofFIG. 1, illustrating a first modification thereto.

FIG. 7 is a schematic circuit diagram of the complete antennaarrangement in accordance with the modification suggested by FIG. 6.

FIG. 8 is a schematic circuit diagram of a second modified form of theinvention.

FIG. 9 is a schematic diagram illustrating the antenna beam pattern andscanning motion associated with the arrangement of FIG. 1.

FIG. 10 is a schematic circuit diagram of the duplexer/transmittercircuits shown in connection with FIGS. 7 and 8.

FIG. 11 is a front elevation view of the antenna as shown in FIG. 3,illustrating the correlation between the four antenna quadrants thereofand the four antenna elements schematically represented in FIG. 4.

DETAILED DESCRIPTION OF THE EMBODIMENT Referring first to FIG. 5 atypical prior art phasescanned antenna arrangement is described. Theantenna itself comprises a fixed four element array including theelements 6a, 6b, 6c and 6d. The antenna structure may be, for example, afour quadrant flat plate slotted array of the type employed with theembodiments of the invention hereinafter disclosed in connection withFIGS. I, 2 and 3. In FIG. 5 a r-f trans mitter 1 operating, for example,in the X-band frequency spectrum, feeds the antenna through a network ofthree I hybrid couplers (magic tees) 2, 3 and 4. The convention employedherein to illustrate such couplers is shown in connection with coupler2. A horizontal line is employed to designate the branching arms BRwhile a vertical line H indicates the H-plane arm of the coupler and adiagonal line E denotes the E-plane arm.

Transmitter I is connected to feed the H-plane arm of the coupler 2while the branching arms of the latter are connected respectively to theH'plane arms of couplers 3 and 4. The E-plane arms of all three couplersare terminated. The branching arms of coupler 3 are connected to feedthe antenna elements 60 and 6!) through a pair of phase shifters 5a and5b respectively. Coupler 4, through its branching arms, feeds antennaelements 6c and 6d through the phase shifters 5c and 5d. Actuating means(not shown) actuate the phase shifters through continuous sinusoidalcycles with each actuation input being offset from the other by 90 as illustrated by the sinusoidal wave forms shown at 7.

The result, shown in FIG. 9, is a beam pattern 79 pro jected by thevertically pointing antenna 10 along a beam axis 81 which is tilted byan angle 6 away from the mechanical boresight 80 of the antenna. As thephase shifters rotate the beam axis 81 rotates through a circular path82 centered about the antenna boresight. The path of the beam axis thusdescribes a cone.

This arrangement has the disadvantage of requiring four separate phaseshifters. These are somewhat complex devices which are difficult tomatch very closely. This means that the antenna system is difficult andexpensive to manufacture when the goal of close tolerance scanning isdesired.

Another type of prior art arrangement includes a sum and differencenetwork connected to feed a four quadrant phase-array antenna of thetype described above. The sum and difference network is the same as thenetwork of couplers shown in FIG. 5 except that a fourth 180 hybridcoupler is connected through its branching arms to the E-plane arms ofthe two output couplers. The E-plane arm of this fourth coupler isterminated.

This sum and difference feed network is driven by a circuit including apair of ferrite modulators employing variable resistances. Thesemodulators must be driven in sync to achieve an accurate conical scan ofthe type depicted in FIG. 9. However, this arrangement also requiresextremely close matching of the dynamic elements (variable resistors)and thus it is difficult economically to achieve high accuracies. Thisleads not only to high cost of manufacturing but also to reducedreliability due to the increased number of complex, dynamic elements.The use of variable resistors also leads to a power loss problem.

Further discussion of the general principles involved in theconstruction of electronic phase-scanned antennas may be found in thetext Introduction to Monopulse by D. R. Rhodes (McGraw-Hill, I959),reference par ticularly being directed to pages 62-68 thereof.

The present invention, hereinafter described. eliminates theaforementioned problems by reducing the number of dynamic circuitelements to a single 360 phase shifter. Since the remaining antennaelements comprise nothing more than passive waveguide structures, whichcan be fabricated to relatively high tolerances at reasonable costlevels, the end result is a low cost antenna system of improvedreliability capable of generating an extremely accurate conical scanpattern.

Referring to FIGS. 1 and 4, an antenna I0 of the flat plate, slottedarray type is connected to an r-f (e.g., X- band) operating device,which may be either a transmitter or receiver, through the microwavenetwork shown. As seen in FIG. I antenna 10 is viewed from the rear.Assuming, for purposes of explanation, that the antenna 10 is beingemployed in the transmission mode, an X-band r-f transmitter (FIG. 4) isconnected to feed a signal to the H-plane arm of an input l hybridcoupler 28. The E-plane arm of this coupler is terminated at 29.

The coupler 28 is connected at one of its branching arms through awaveguide 26 to a 360 mechanical phase shifter 22. The output of thephase shifter is connected to the lower right-hand port ofa hybridcoupler 20. A drive motor 24 is connected to continuously rotate theshifter 22 through 360.

The upper ports of the 90 coupler 20 and the other branching arm of the[80 coupler 28 are connected to a sum and difference network comprisingfour 180 hybrid couplers I2, l4, l6 and 18. The branching arms ofcoupler 18 are connected to the H-plane arms of the couplers I2 and 14by a pair of wave guides 30 and 32 respectively. The E-plane arms ofcouplers l2 and 14 are connected to the branching arms of coupler I6,the E-plane arm of the latter being terminated at 17.

The H-plane arm of coupler 16 is fed by the upper right-hand port of the90 coupler 20 while the upper left-hand port of the latter is connectedto feed the E- plane arm of coupler 18. The lower left-hand port ofcoupler 20 is terminated. The final input connection to the sum anddifference network is through waveguide 34 which connects the left-handbranching arm ofinput coupler 28 to the H-plane arm of coupler 18.

As previously mentioned the dashed lines 34, 36, 38, 40, 42, 44 and 46of FIG. 1 represent conventional waveguide connections which connectionsfor purposes of clarity have been omitted from the drawing.

The branching arms of couplers l2 and 14 are connected to feed the fourquadrants of antenna 10. Four closed-ended waveguide elements 41, 43, 45and 47 are mounted on the rear plate I] of antenna 10 to couple energyto the antenna through a series of coupling slots described in moredetail subsequently in connection with FIGS. 2 and 3. The branching armsof coupler I2 are connected to waveguides 45 and 47 by waveguides 44 and46 respectively. Similarly, the branching arms of coupler I4 areconnected to waveguides 41 and 43 by waveguides 40 and 42 respectively.

Referring to FIGS. 2 and 3, the specific structure of antenna I0 ishereinafter described in detail. FIG. 2 is a cross section of theantenna structure view from the front of the antenna along the line 2-2of FIG. 1. FIG. 3 is a front elevation view of the full antenna withfront plate 13 in place.

As shown in FIG. 2 the rear plate 11 and the front plate 13 of theantenna are spaced apart by a series of waveguide partitions 51, 53 and57. The outer periphery of the structure is enclosed by side walls 55.Partitions SI and 53 divide the antenna into four equal quadrants. Anadditional series of horizontally running partitions 57 divides eachquadrant into four sections. Each of the four antenna quadrants isdepicted in the schematic circuit diagram of FIG. 4 as one of the fourantenna array elements 10a, 10b, 10c and lOd. FIG. 11 illustrates themanner in which the four array elements correspond to the four quadrantsof the structure of FIGS. 2 and 3.

Waveguide 45 (FIG. 2) is coupled to the four sections of quadrant 10a bya series of coupling slots 59a formed in the rear plate 11. Similarly,waveguide 47 is coupled to the four sections of quadrant b by a seriesof coupling slots 5912 while waveguide 41 is coupled to quadrant 10cthrough the four slots 59c and waveguide 43 is coupled to quadrant 10dby the four slots 59d. The front plate 13 of the antenna (FIG. 3) isprovided with a series of parallel radiating slots 61 associated withthe several quadrant sections.

As shown in FIG. 4, a phase adjuster 37 may be inserted in the waveguide36 which connects the 90 coupler with the E-plane arm of 180 coupler 18to facilitate the electrical equalization of waveguides 36 and 38 (i.e.,enables the nulling of any relative phase shifts imposed by thewaveguides).

In operation, the application by transmitter 70 (FIG. 4) of X-bandradiation to the antenna system results in the transmission by theantenna ofa beam such as illustrated at 79 in FIG. 9. The beam 79 istilted from the mechanical boresight 80 of the antenna by an angle 6 androtates through a conical path defined by the circle 82 as the phaseshifter 22 rotates. Each full revolution of the shifter results in onecomplete scan (revolution) of the bean. The simplest manner ofcompletely describing the operation of the various circuit elements ofthe embodiment depicted in FIG. 4 is to mathematically describe thevector voltage present at each significant point of the circuit asdenoted by the letters A through N shown in FIG. 4. The point A taken atthe output of transmitter 70 represents the antenna system input voltageE. The voltages at the remaining circuit points are as follows:

where d) instantaneous phase of the rotating phase shifter It should benoted that the output voltage at each of the four antenna elementsincludes a constant term and a variable term of equal magnitude to theconstant term but which varies in phase in accordance with the operationof the phase shifter 22. The phase variance of the voltage at theantenna elements K, L, M and N progressively differs by voltage at theantenna elements K, L, M and N progressively differs by 90. The netresult is the conical scan pattern illustrated in FIG. 9. It should befurther noted that the characteristics of the circuit are fullyreciprocal and that a receiver may be substituted for transmitter 70.The response characteristics of the antenna to received radiation, asseen from the receiver, will be conically scanned. Also, the scan angle0 (FIG. 9) may be adjusted by varying the ratio of energy directed towaveguides 26 and 34 from the transmitter 70. To this end a directionalcoupler having the desired characteristics may be substituted for 180hybrid coupler 28 (which divides the input energy equally). Channellingall the energy to waveguide 34 results in a beam axis coinciding withthe mechanical boresight of the antenna. Channelling most (but not all)the energy into waveguide 26 results in a maximum scan angle.

FIGS. 6 and 7 illustrate a first modified embodiment of the inventionwherein the system is arranged to receive as well as transmit. Duringtransmission a fixed (non-scanned) beam pattern is directed along themechanical boresight of the antenna and during the receive operation(between transmission intervals) the response pattern of the antenna isconically scanned.

FIG. 6 shows only the modified portion of the structure. The remainderof the circuit is identical to that shown in FIG. I. The modificationcomprises addition ofa duplexer 65 which is connected to the leftbranching arm of 180 hybrid coupler 28'. The remaining primed referencenumerals shown in FIG. 6 indicate structural identity between theassociated elements and those represented by corresponding numbers inFIG. I. As shown in FIG. 7 the duplexer 65 is inserted in waveguide 34which connects the left branching arm of coupler 28 to the H-plane armof coupler 18'. A receiver 67 is connected to the H-plane arm of coupler28 and a transmitter 70 is connected to feed an input to the duplexer. Apulsing circuit 71 cooperates with transmitter 70' so that the ouptutfrom the latter is a series of signal pulses. With the duplexer in theposition shown the effects of the continuously rotating phase shifter22' are not imposed on the transmitted energy and the result isgeneration of an antenna beam pattern which has its axis in alignmentwith the antenna boresight and which does not rotate.

However, when the transmission pulse terminates the operation ofduplexer 65 is to return received energy through waveguide 34 to theleft branching arm of coupler 28' in the same manner as previouslydescribed in connection with FIG. 4, just as though the transmit ter wasnot in the circuit. Thus, the aforedescribed conical scanning operationis realized during the receive mode.

FIG. 10 schematically illustrates the structure and operation of theduplexer 65. A ferrite circulator 65a rotates input energy in aclockwise direction so that the output from transmitter 70' is coupledupwards in the direction of arrow 75 into the section of waveguide 34'which connects to coupler 18'. When the transmitter is not operating,energy received from coupler 18' is coupled through the circulator inthe direction of arrow 76 into a transmit/receive tube 65b and thence tothe lower section of waveguide 34 which connects to the coupler 28'.Transmit/receive tube 65!) isolates the receiver from the high levelenergy generated by the transmitter 70'.

A second modified embodiment of the invention is shown in FIG. 8. Thecircuit there illustrated is identical to that of FIG. 4 except aduplexer 65' is inserted in front of the H-plane arm of input/outputcoupler 28". The duplexer 65', as with the duplexer 65 shown in FIG. 7,allows the antenna system to operate in both a transmit and receivemode. However, with the duplexer positioned as shown in FIG. 8 both thetransmitted and received energy is conically scanned. The operation ofthe pulser 7|, transmitter 70". duplexer 65 and receiver 67' isidentical to that set forth above for the pulser 71, transmitter 70,duplexer 65 and receiver 67. The only difference is that due to theposition of the duplexer 65' both the transmitted as well as the received signals are acted upon by the rotating phase shifter 22" in themanner previously described in connection with FIG. 4.

It will be appreciated that various additional changes in the form anddetails of the above-described preferred embodiments may be effected bypersons of ordinary skill without departing from the true spirit andscope of the invention.

1 claim:

I. A phase-scanned r-f antenna comprising, in combination:

a four quadrant antenna;

first and second 180 hybrid couplers connected to said antenna, the fourbranching arms of said cou plers being connected to different ones ofsaid antenna quadrants;

a third 180 hybrid coupler having its branching arms connected to theE-plane arms of said first and second couplers;

a fourth 180 hybrid coupler having its branching arms connected to theH-plane arms of said first and second couplers;

a 90 hybrid coupler having one pair of adjacent ports connected to the Hand E-plane arms of said third and fourth 180 hybrid couplersrespectively;

a fifth 180 hybrid coupler having its branching arms connectedrespectively to the H-plane arm of said fourth 180 coupler and to a portof said 90 cou pler which is opposite the port connected to said third180 coupler.

a phase shifter connected in the circuit between the branching arm ofsaid fifth 180 coupler and said 90 coupler;

r-f energy operating means connected to the H-plane arm of said fifth180 coupler; and

means for actuating said phase shifter whereby the axis of the beampattern of said antenna is caused to scan in a path describing at leasta segment of a cone.

2. The phase-scanned r-f antenna set forth in claim 1 wherein saidactuating means operates said phase shifter through 360 whereby the axisof the beam pattern of said antenna is caused to scan in a path describing a cone.

3. The phase-scanned r-f antenna set forth in claim 1 wherein said r-fenergy operating means comprises a transmitter.

4. The phase-scanned r-f antenna set forth in claim 3 wherein saidtransmitter is constructed and arranged to transmit r-f energy in theX-band frequency range.

5. The phase-scanned r-f antenna set forth in claim 1 wherein said r-fenergy operating means comprises a receiver.

6. The phase-scanned r-f antenna set forth in claim 5 wherein saidreceiver is constructed and arranged to receive and detect r-f energy inthe X-band frequency range.

7. The phase-scanned r-f antenna set forth in claim 5 furthercomprising:

a duplexer connected between said l-l-plane arm of said fourth 180hybrid coupler and the branching arm of said fifth 180 hybrid coupler;

an r-f transmitter coupled to said duplexer to feed a signal to saidantenna; and

means for intermittently energyzing said transmitter to cause saidantenna to emit a fixed beam pattern. said receiver operating during theintervals between said transmissions to receive and detect signals froma field which is conically scanned by the operation of said phaseshifter.

8. The phase-scanned r-f antenna set forth in claim 5 furthercomprising:

a duplexer connected between said receiver and said H-plane arm of saidfifth 180 hybrid coupler;

an r-f transmitter coupled to said duplexer to feed a signal to saidantenna; and

means for intermittently energyzing said transmitter to cause saidantenna to emit a beam pattern which is conically scanned by theoperation of said phase shifter, said receiver operating during theintervals between said transmissions to receive and detect signals froma field which is also conically scanned by the operation of said phaseshifter.

1. A phase-scanned r-f antenna comprising, in combination: a fourquadrant antenna; first and second 180* hybrid couplers connected tosaid antenna, the four branching arms of said couplers being connectedto different ones of said antenna quadrants; a third 180* hybrid couplerhaving its branching arms connected to the E-plane arms of said firstand second couplers; a fourth 180* hybrid coupler having its branchingarms connected to the H-plane arms of said first and second couplers; a90* hybrid coupler having one pair of adjacent ports connected to the Hand E-plane arms of said third and fourth 180* hybrid couplersrespectively; a fifth 180* hybrid coupler having its branching armsconnected respectively to the H-plane arm of said fourth 180* couplerand to a port of said 90* coupler which is opposite the port connectedto said third 180* coupler. a phase shifter connected in the circuitbetween the branching arm of said fifth 180* coupler and said 90*coupler; r-f energy operating means connected to the H-plane arm of saidfifth 180* coupler; and means for actuating said phase shifter wherebythe axis of the beam pattern of said antenna is caused to scan in a pathdescribing at least a segment of a cone.
 2. The phase-scanned r-fantenna set forth in claim 1 wherein said actuating means operates saidphase shifter through 360* whereby the axis of the beam pattern of saidantenna is caused to scan in a path describing a cone.
 3. Thephase-scanned r-f antenna set forth in claim 1 wherein said r-f energyoperating means comprises a transmitter.
 4. The phase-scanned r-fantenna set forth in claim 3 wherein said transmitter is constructed andarranged to transmit r-f energy in the X-band frequency range.
 5. Thephase-scanned r-f antenna set forth in claim 1 wherein said r-f energyoperating means comprises a receiver.
 6. The phase-scanned r-f antennaset forth in claim 5 wherein said receiver is constructed and arrangedto receive and detect r-f energy in the X-band frequency range.
 7. Thephase-scanned r-f antenna set forth in claim 5 further comprising: aduplexer connected between said H-plane arm of said fourth 180* hybridcoupler and the branching arm of said fifth 180* hybrid coupler; an r-ftransmitter coupled to said duplexer to feed a signal to said antenna;and means for intermittently energyzing said transmitter to cause saidantenna to emit a fixed beam pattern, said receiver operating during theintervals between said transmissions to receive and detect signals froma field which is conically scanned by the operation of said phaseshifter.
 8. The phase-scanned r-f antenna set forth in claim 5 furthercomprising: a duplexer connected between said receiver and said H-planearm of said fifth 180* hybrid coupler; an r-f transmitter coupled tosaid duplexer to feed a signal to said antenna; and means forintermittently energyzing said transmitter to cause said antenna to emita beam pattern which is conically scanned by the operation of said phaseshifter, said receiver operating during the intervals between saidtransmissions to receive and detect signals from a field which is alsoconically scanned by the operation of said phase shifter.